This invention relates to a low temperature process suitable for forming stress-reduced thin films onto a ballistically alloyed substrate in a high vacuum, hydrogen-free atmosphere, the coated article formed by the process and the accompanying apparatus. More particularly, the invention relates to a method which simultaneously utilizes a low energy sputtered beam and a high energy bombarding beam to ballistically alloy the surface of a substrate and thereafter simultaneously utilize the low energy sputtered beam and a high energy beam to produce thin, pure, stress-reduced hard films such as polycrystalline diamond; the deposited coatings being bonded to the substrate within a thin, boundary zone in which the deposited layer has physically mixed and/or chemically bonded onto the ballistically alloyed surface of the substrate.